1. Field of the Invention
The present invention relates to a high voltage power supply apparatus used in a laser printer, a multifunction printer, and so on, and more particularly, to a high voltage power supply apparatus, which can vary the magnitude of current output therefrom according to environmental conditions and uniformly output the current irrespective of the characteristics of the electronic devices used therein, and a method of correcting the current output from the apparatus.
2. Description of the Related Art
Multifunction printers or laser printers scan a laser beam on an electro statically charged, photoconductive drum to produce latent characters or images of a page on the drum and transfer toner to printing paper to develop the latent characters or images. The multifunction printers or laser printers fix the developed characters or images to the printing paper and output printed matter with the characters or images.
Multifunction printers or laser printers use a high voltage in order to perform the above operations. To obtain the high voltage, the multifunction printers or laser printers employ a high voltage power supply apparatus. Such a high voltage power supply apparatus includes a signal input unit, a switching control unit, a switching unit, and a fly back transformer to output the high voltage current. The signal input unit receives from a central processing unit (CPU) an enable signal indicating whether to output a high voltage. The switching control unit outputs, in response to the enable signal, a control signal to drive the switching unit. The switching unit generates a voltage on a primary side of the fly back transformer in response to the control signal output from the switching control unit. The fly back transformer boosts the voltage generated in a coil on the primary side thereof, rectifies the high voltage, and outputs the rectified voltage via an output terminal of a coil on a secondary side thereof.
According to the conventional art, the CPU simply determines whether to turn on or off current output from the high voltage power supply apparatus without regard to environmental conditions and outputs the enable signal on the basis of the determination, and the high voltage power supply apparatus turns on or off the current in response to the enable signal. Because the conventional high voltage power supply apparatus cannot control the output current according to environmental conditions, e.g., temperature and humidity, it is difficult to create a uniform electric potential on the surface of the photoconductive drum and ensure a high quality image. The conventional high voltage power supply apparatus has another disadvantage in that the output current cannot be uniformly output from the fly back transformer due to the characteristics of an electronic device used in the apparatus or other reasons.
If a distance between circuits is not sufficient due to miniaturization of a high voltage power supply apparatus and space reduction and functional enhancement of a printed circuit board (PCB), voltage induction may occur between the circuits and the circuits may malfunction due to noise. In particular, since high voltages used by laser printers are output from multiple output terminals, an abnormal high voltage is output from an output terminal due to an influence of a high voltage generated by another output terminal, when the high voltage power supply apparatus does not receive a pulse width modulation signal.